The present invention relates to gas lasers and, more particularly, to a gas laser having a barrier which prevents particulate matter expected to emanate from a surface of a laser component from depositing on a face of an optical element of the laser. (As used herein, the term "gas laser" is meant to encompass both gas and gas ion lasers.) It also relates to a method for protecting the face of such an optical element from particulate matter expected to emanate into the laser optical cavity. It is particularly applicable to an internal mirror laser of the type in which a sealed tube having interior mirror faces is positioned in the optical cavity.
The output power of a gas laser, i.e., the power of the output beam of optical radiation, is greatly affected by the integrity of the faces of optical elements which interact with the optical radiation from which the output beam is formed. This is especially true if the optical element faces are within the same volume which the optical radiation is generated. For example, there is a class of ion lasers which are referred to as internal mirror lasers. In such a laser, the mirrors (or reflectors) for the optical radiation are sealed at the ends of the tube which contains the active gas medium. If deposits or other surface degradation should occur to the face of one or both of the mirrors within the tube, it is generally not possible to clean the same without affecting the integrity of the tube. Contamination of such a mirror face can result in significant decrease in the power of the output beam. This low power level can either result in a rejection of the laser tube at the time of manufacture, or can result in the tube itself having a shorter useful life because the current that must be applied to the tube to reach a required power output is high.
A technique has been developed for aligning the mirrors within an internal mirror construction which can exacerbate the situation. That is, it is common to provide a mirror holder on the tube at each end with a circumferentially weakened wall section which enables the same to be deformed or bent to change the angle on which the optical radiation impinges on the mirror. U.S. Pat. No. 3,826,998 provides a good discussion of this approach. A variation on this approach is described in U.S. Pat. No. 4,217,559. Deformation of the mirror holder at the weakened section results in the surface of the holder at the weakened section interiorly of the tube developing stress during a bending compressive stress on one side and tensile stress on the other side). The result of deformation of this section is that the section surface within the tube gives off particulate matter. Such particulate matter contaminates the inside of the tube and, it is postulated, is transported by the optical radiation to the mirror faces on which such optical radiation impinges. Contamination of these faces reduces the power output. While this phenomenon is not noticeable in low power internal mirror lasers, it is a significant problem for high power lasers of this type.